2010/5/21 James Courtier-Dutton james.dutton@gmail.com
On 20 May 2010 10:41, Sebastian H. vand2@gmx.de wrote:
That's clear. I imagined that maybe the dB scale could be the "real thing" and the
volume
steps would be a convenient but possibly coarse mapping into a denser stepped dB space provided by the hardware/driver. This was unlikely but I wanted to ask anyway ;-).
I believe it could be extended to support a continuous range. For example, some hardware uses a 32bit value to control the gain. The mix operation is simply "the_sample" * "the_control_value". So in this case the hardware has a linear control that can be considered continuous for our purposes. The conversion from the control value to a usable value would have to include a user land log operation. It was never implemented due to lack of demand. For the cards that do have this 32bit linear value, a simple lookup table is used in the kernel code to convert it to 256 step values. If implemented, one could then introduce professional gain controls that do not produce "clicks" in the output when adjusted. gain controls with steps in them produce clicks when the gain control is adjusted.
I thinks Sebastian's question is whether he can use snd_mixer_selem_set_playback_ dB() set any values in between the volume steps
e.g. Master volume control of ac97 is 1.5 dB per step,
when using snd_mixer_selem_set_playback_dB() to set -0.9dB , how can the mixer application know what dB value has been set since the value is in between -1.5dB and 0dB without snd_mixer_selem_get_playbackdB()